Yoshida - 1981 - Fundamentals of Rice Crop Science

12 FUNDAMENTALS OF RICE CROP SCIENCE
method of counting leaves, particularly when the reader refers to works published
in Japan. The first leaf, however, is known to have the same anatomical characteristics
as succeeding leaves (Hoshikawa 1973).
In experiments, the leaf on the main culm is marked with dots of white or red
enamel and the observation date is recorded. The n th leaf on the main culm is
described as n/0, where 0 implies the main culm. Thus, 3/0 refers to the third leaf
on the main culm. In this way, the leaf number can be recorded and related to the
calendar day. When the first leaf is fully developed, the plant age is counted as 1.0.
Similarly, when the second leaf attains its maximum elongation, the plant age is
2.0, and so on. A leaf is considered to have fully developed when the tip of the
succeeding leaf emerges. In cases where observations must be made before a leaf’s
elongation is complete, leaf age may be estimated by the ratio of the length of an
elongating leaf to that of the preceding leaf. For instance, if the 6th leaf is still
elongating and its length is estimated at about 50% the length of the 5th leaf, the
plant’s age is 5.5. This estimation is, however, subject to error because the two
leaves are not of the same length. Recording the time of maximum leaf elongation
is more accurate.
1.3.3. Seed reserve for seedling growth
At initial stages of seedling growth, growth of the coleoptile and subsequent leaves
is largely dependent on the seed reserve — nutrients accumulated in the endosperm.
When a seed germinates and grows in the dark, it continues to grow until the
tip of the 4th leaf emerges (Fig. 1.10). Darkness induces extraordinary elongation
of the mesocotyl (the axis between the node of the coleoptile and the base of the
radicle), the coleoptile, the first and second leaves, and the first and second
internodes.
1.10. Rice seedling growth in the dark
(Hoshikawa 1975). The reserved nutrients
of the seed support seedling growth up to
the third leaf.